1. Field of the Invention
The present invention relates to a polishing apparatus for use in polishing a semiconductor substrate and more particularly to a polishing apparatus which allows recycling of slurry on the polishing pad.
2. Description of the Related Art
Generally, to reduce the cost in polishing processes, abrasives or slurries (liquid abrasives) containing abrasives are recycled for repeated use.
An abrasive has been suggested which is suitable for such recycling in that the abrasive provides less reduction in efficiency of polishing and secures a sufficient rate of polishing when recycled (Japanese Patent Laid-Open Publication No. Hei 4-313224). On the other hand, various techniques for recycling slurries have been suggested (Japanese Patent Laid-Open Publications No. Hei 7-156045 and No. Hei 9-314466, and Japanese Patent No. 2903980).
FIG. 1 illustrates a prior-art ultrasonic abrasives polishing apparatus disclosed in Japanese Patent Laid-Open Publication No. Hei 7-156045. An ultrasonic propagation liquid 106 is filled in an ultrasonic propagation tank 105 with an ultrasonic vibrator 102 arranged on the bottom thereof. In addition, an abrasive tank 100 in which an abrasive liquid 101 is filled is immersed in the ultrasonic ropagation liquid 106 in the ultrasonic propagation tank 105. The abrasive liquid 101 is adapted to return to an agitator tank 103 via a pipe and a valve, which are provided under the bottom of the abrasive tank 100. In the agitator tank 103, provided is a magnetic separator 104 for filtering out foreign substances in the abrasive liquid. After the foreign substances in the abrasive liquid 101 have been filtered out, the abrasive liquid 101 stored in the agitator tank 103 is forced by a pump 107 to a vacuum deaerator 108, where the abrasive liquid 101 is deaerated by the vacuum deaerator 108. Thereafter, the abrasive liquid 101 is fed to the abrasive tank 100. Thus, the abrasive liquid 101 is circulated for use.
In addition, in Japanese Patent Laid-Open Publication No. Hei 9-314466, disclosed is a semiconductor wafer polishing apparatus which filters out impurities in an abrasive liquid to circulate the abrasive liquid. FIG. 2 is a schematic view illustrating the prior-art polishing apparatus. In the polishing apparatus, a platen 112, to the upper surface of which a polishing pad 113 is affixed, is adapted to be rotationally driven by rotary drive means (not shown). A weight 111 is adapted to press a wafer 110 against the upper surface of the platen 112. Under the platen 112, provided is a slurry pan 114 for receiving a slurry 116 drained from the polishing pad 113. The slurry pan 114 is coupled to a slurry tank 117 via a slurry collecting pipe 115. The lower end of a feed pipe 122 is immersed in the slurry 116 in the slurry tank 117. The feed pipe 122 is connected to heavy metal ion filter means 120 via a pump 121. Heavy metal ions generated during polishing are trapped and filtered out with the filter means 120, and thereafter the slurry 116 is fed through the feed pipe 122 onto the polishing pad 113 from a slurry feed port 119. Incidentally, the heavy metal ion filter means 120 comprises a column with polymers filled and sealed therein, being adapted to filter out heavy metal ions with the polymers. Thus, the slurry 116 is circulated for use.
FIG. 3 illustrates a prior-art polishing apparatus described in Japanese Patent No. 2903980. There are provided a reservoir 136 for storing a slurry 131 at the center of a platen 137 and a polishing pad 138 on the upper surface of the platen 137. A wafer 130 is adapted to be pressed against the polishing pad 138. On the outer circumference surface of the platen 137, a funnel 139 for collecting the slurry is provided around the platen 137. Further outside the funnel 139, provided is a receiver tank 140 for receiving a spill-over of the spilt slurry 131. In addition, a waste liquid tank 132 collects a waste liquid, which has been used for polishing, from the receiver tank 140. The slurry waste liquid in the waste liquid tank 132 is drained to the outside via a drain pipe (not shown). In addition, the slurry 131 collected in the funnel 139 returns to the reservoir 136 through a pipe 141 which connects the funnel 139 to the reservoir 136. This allows the slurry 131 to be recycled.
A slurry tank 135 stores the slurry 131, which is fed to the reservoir 136 by means of a pump 133. Furthermore, the slurry 131 in the reservoir 136 is fed onto the polishing pad 138 by means of a pump 134.
In this prior art, only the same amount of the slurry 131 as that used for polishing is fed by the pump 134 from the reservoir 136 onto the polishing pad 138. The slurry 131 collected in the funnel 139 is returned by a pump (not shown) to the reservoir 136 through the pipe 141. The slurry collected in the receiver tank 140 is then collected in the waste liquid tank 132. Only the same amount of slurry as that of the slurry drained to the waste liquid tank 132 is fed from the slurry tank 135 to the reservoir 136 by means of the pump 133. This allows the level of the liquid to be kept generally constant in the reservoir 136. That is, the polishing apparatus collects, for recycling, part of the waste liquid that has been used for polishing and drains the remaining waste liquid to the waste liquid tank 132, the remaining waste liquid being then disposed of outside. Thus, part of the slurry 131 is circulated for use.
However, any one of the prior art polishing apparatuses described above needs to be provided with a circulation system for circulating the slurry. This presents a problem of limiting the reduction in cost of facilities in the polishing process .
Furthermore, the polishing apparatus described in Japanese Patent No. 2903980 recycles only part of the waste liquid after polishing. This also presents a problem of limiting the reduction in cost of slurries.
An object of the present invention is to provide a polishing apparatus which provides reduced processing cost in the polishing process and obviates the need for a slurry circulation system.
The polishing apparatus according to the present invention comprises a polishing pad to be rotationally driven for polishing a ground material; a ground material carrier for sustaining the ground material; slurry feed means for feeding a slurry onto the polishing pad; a filter, disposed upstream from the ground material in a direction of rotation of the polishing pad, for trapping swarf generated on the polishing pad; and a defense barrier, provided around the polishing pad, for retaining the slurry on the polishing pad during polishing, for allowing the slurry on the polishing pad to be drained to outside after polishing is completed.
According to the present invention, the slurry fed onto the polishing pad by the slurry feed means is prevented from spilling out therefrom and thus retained on the polishing pad. Then, the swarf generated during polishing diffuses into the slurry, however, the swarf is trapped by the filter, thereby allowing the ground material to be always ground with a clean slurry from which the swarf has been removed. Then, after the polishing is completed, the slurry on the polishing pad is allowed to flow out therefrom and thus drained. As described above, according to the present invention, the swarf generated on the polishing pad is trapped by the filter on the polishing pad, and the defense barrier retains the slurry on the polishing pad to polish the predetermined number of ground materials. This allows the slurry to be recycled on the polishing pad, thereby reducing the processing cost in the polishing process. Furthermore, according to the present invention, devices such as a circulation system provided for a prior art polishing apparatus for circulating the slurry is not required, except for the polishing apparatus. This reduces the cost of facilities in the polishing process.
In this case, the conditioning portion for conditioning the polishing pad can also be provided on the polishing pad. The conditioning can serve to always maintain the polishing pad under a good polishing condition, and the swarf or the like generated during the conditioning is trapped by the filter.
Furthermore, the projected member, to which the ring-shaped polishing pad fits, is provided at the center of the surface of the base on which the polishing pad is placed. The slurry on the polishing pad is thereby prevented from spilling out therefrom by means of the defense barrier and the projected member, and is thus retained on the polishing pad. That is, the slurry is prevented from spilling out from the ring-shaped polishing pad and allowed to flow in conjunction with the polishing pad.
Furthermore, the defense barrier is preferably supported by the base so as to be tilted outwardly to open further downwardly than the surface of the polishing pad. This makes it easy to drain the slurry.
Still furthermore, the filter can be adapted to be sustained by the ground material carrier and can have a structure of lattice-like multi-layers made of polyester fiber or polyamide fiber.
The nature, principle, and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.